1. Field of the Invention
This invention relates to an improved one-piece flexible seal for overpressure vent structure used to protect a confined space that meets regulated hygienic standards. The vent structure has a vent aperture for relief of high predetermined overpressure conditions. The pressure relieving apparatus has frame structure that supports a vent membrane unit provided with a series of slots defining a relief area of the vent membrane unit. The seal is adapted to be positioned between a frame member of the frame structure and a peripheral portion of the vent membrane unit. A single seal performs the dual function of preventing leakage of fluid between the frame member and the vent membrane unit while maintaining an effective seal during positive and negative pressure cycling of the vent membrane unit during use of the vent structure.
2. Description of the Prior Art
Explosion vents traditionally have been provided with a rupturable sheet of metal that has interrupted slots presenting a line of weakness defining the outline of the relief area of the vent. The amount of overpressure required to open the relief are of the vent is determined by, among other things, the type, thickness, and physical properties of the metal selected for fabrication of the explosion vent, the nature of the line of weakness, and the location of the line of weakness in the overall area of the vent. The thickness of the metal vent material is limited in certain instances by regulatory standards to no more than about 0.060 in. Furthermore, a thin layer of a thermoplastic polymeric material, such as fluorinated ethylene propylene (FEP), or an equivalent, such as PTFE or PFA, is provided in association with the metal material to cover the slots forming the line of weakness.
In those instances where the explosion vent is used to protect structures in industries where the processing equipment, conduits, vessels, and the like are necessarily operated under sanitary conditions, frequent hygienic cleaning, using a cleansing agent such as steam, is mandated by regulations and carried out in accordance with recognized procedures. It is conventional practice to provide a flexible seal between the vent membrane unit and supporting frame structure. It can be appreciated that in cleaning the processing equipment structures, it is essential that all residue remaining from a particular process be removed before equipment can be placed back in operation. It is especially difficult to displace and remove particulate materials from cracks and crevices in the components of the equipment being cleaned.
Very often, the vent apparatus is mounted in an operative upright position in the sidewall of processing apparatus or components thereof that are being protected from an overpressure condition. Accordingly, removal of particulate material that may collect along the lower edge of generally rectangular vent apparatus between a flexible seal and the lowermost frame member of the vent apparatus is especially difficult. This is particularly so when the seal employed is of typical transverse P-shape having a tubular segment that is unitary with a flat dependent skirt. Elongated seals of the P type are placed between a peripheral edge of the vent membrane and an opposed frame member of the vent apparatus frame structure, with the tubular segment being compressed between the vent and the frame member, while the skirt portion provides additional sealing surface between the process and the surrounding atmosphere.
Particulate material and the like generated by the process collects in the peripheral crevice formed between the vent membrane and the tubular portions of the P seal. In the case of a vertically mounted vent, a disproportionate portion of residual processing particulate material tends to collect in the lowermost horizontal crevice between the tubular P seal and the vent membrane unit and the adjacent upright corners of the P seal, than is the case of the remaining crevice between the P seal and the support frame structure. Removing particulate material that has lodged in the lowermost horizontal crevice between the P seal and the support frame structure, even with high pressure steam ejection cleaning equipment, is particularly difficult. Not only is it time-consuming to attempt removal of all of the residual particulate material residing in the crevices between the P seal and the vent frame structure, but often times, as a practical matter, steam dislodgement of the residual particulate material is not, in fact, totally effective.
Therefore, there is a long-existing, unsolved need for an improved seal to be interposed between the periphery of a vent membrane and supporting frame structure that is especially useful for sanitary processing equipment in which cleaning of the vent structure may be more effectively accomplished in a shorter period of time than in the past where P-type seals have conventionally been employed.